pgsql: Fix const qualification in prune_freeze_setup()

Fix const qualification in prune_freeze_setup()

The const qualification of the presult argument to prune_freeze_setup()
is later cast away, so it was not correct. Remove it and add a comment
explaining that presult should not be modified.

Author: Peter Eisentraut <peter@eisentraut.org>
Reviewed-by: Melanie Plageman <melanieplageman@gmail.com>
Discussion: https://postgr.es/m/fb97d0ae-a0bc-411d-8a87-f84e7e146488%40eisentraut.org

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4877391ce894e5b964a69e94e1750cde9df04a07

Modified Files
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src/backend/access/heap/pruneheap.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)